This invention relates to a remaining capacity computation system wherein a connected electrical equipment unit detects current, the detected current is sent to a remaining capacity computation apparatus via a communication circuit, the remaining capacity computation apparatus computes remaining capacity from the received current, and the computed remaining capacity is sent to the connected electrical equipment unit via the communication circuit. In particular, this invention relates to a remaining capacity computation system wherein the connected electrical equipment unit and the remaining capacity computation apparatus are connected by a one line communication circuit.
Accurate computation of remaining battery capacity for portable electrical equipment using a battery as a power supply allows their convenient use. In particular, for proper operation of equipment such as a laptop computer, a prescribed shutdown procedure and power-down is required prior to complete battery discharge. Remaining battery capacity is computed by integrating charging current and discharging current flowing through the battery. The integrated value of charging current is added to the remaining capacity, and the integrated value of discharging current is subtracted from the remaining capacity.
To realize this, a system has been developed which provides a current detection section in the connected electrical equipment unit, and a remaining capacity computation section in the battery pack which houses the battery. In this system, the remaining capacity computation section contained in the battery pack accurately computes remaining battery capacity with high precision. This is because the remaining capacity computation section calculates remaining capacity of the battery under optimum conditions. Further, since the current detection section is housed in the connected electrical equipment unit, this system has the characteristic that the battery pack, which is discarded when it becomes unusable, can be made inexpensively. However, this system requires communication between the connected electrical equipment unit and the remaining capacity computation section. This is because the connected electrical equipment unit sends a current signal to the remaining capacity computation section, and the remaining capacity computation section computes and sends a remaining capacity signal to the connected electrical equipment. To keep the communication circuit as simple as possible, it is necessary to send the detected current signal and the remaining capacity signal in both directions via a one line communication circuit. However, a one line communication circuit cannot send the detected current signal and the remaining capacity signal at the same time. For example, the remaining capacity signal can be sent in the following manner.
(1) A detected current signal is sent from the connected electrical equipment unit to the remaining capacity computation section at fixed periodic intervals, and a request signal is issued whenever the remaining capacity is needed. When the remaining capacity computation section receives a request signal, it sends a remaining capacity signal to the connected electrical equipment unit.(2) A detected current signal is sent from the connected electrical equipment unit to the remaining capacity computation section at fixed periodic intervals, while the remaining capacity computation section sends a remaining capacity signal to the connected electrical equipment unit at fixed periodic intervals without depending on a request signal.
However in system (1) described above, there are times when the signal to send detected current from the connected electrical equipment unit to the remaining capacity computation section and the signal to request output of remaining capacity can be sent simultaneously. In system (2) as well, the detected current signal from the connected electrical equipment unit and the remaining capacity signal from the remaining capacity computation section can be output at the same time. Consequently, while accurate battery current can be detected, the remaining capacity signal cannot be reliably sent to the connected electrical equipment unit.